.\" $OpenBSD: mbtowc.3,v 1.3 2010/11/20 18:23:19 stsp Exp $
.\" $NetBSD: mbtowc.3,v 1.5 2003/09/08 17:54:31 wiz Exp $
.\"
.\" Copyright (c)2002 Citrus Project,
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.Dd $Mdocdate: November 20 2010 $
.Dt MBTOWC 3
.Os
.\" ----------------------------------------------------------------------
.Sh NAME
.Nm mbtowc
.Nd converts a multibyte character to a wide character
.\" ----------------------------------------------------------------------
.Sh SYNOPSIS
.Fd #include <stdlib.h>
.Ft int
.Fn mbtowc "wchar_t * restrict pwc" "const char * restrict s" "size_t n"
.Sh DESCRIPTION
The
.Fn mbtowc
usually converts the multibyte character pointed to by
.Fa s
to a wide character, and stores it in the wchar_t object pointed to by
.Fa pwc
if
.Fa pwc
is non-null and
.Fa s
points to a valid character.
This function may inspect at most n bytes of the array beginning from
.Fa s .
.Pp
In state-dependent encodings,
.Fa s
may point to the special sequence bytes to change the shift-state.
Although such sequence bytes correspond to no individual
wide-character code,
.Fn mbtowc
changes its own state by the sequence bytes and treats them
as if they are a part of the subsequence multibyte character.
.Pp
Unlike
.Xr mbrtowc 3 ,
the first
.Fa n
bytes pointed to by
.Fa s
need to form an entire multibyte character.
Otherwise, this function causes an error.
.Pp
Calling any other functions in
.Em libc
never change the internal
state of the
.Fn mbtowc ,
except for calling
.Xr setlocale 3
with the
.Dv LC_CTYPE
category changed to that of the current locale.
Such
.Xr setlocale 3
calls cause the internal state of this function to be indeterminate.
.Pp
The behaviour of
.Fn mbtowc
is affected by the
.Dv LC_CTYPE
category of the current locale.
.Pp
These are the special cases:
.Bl -tag -width 012345678901
.It s == NULL
.Fn mbtowc
initializes its own internal state to an initial state, and
determines whether the current encoding is state-dependent.
This function returns 0 if the encoding is state-independent,
otherwise non-zero.
In this case,
.Fa pwc
is completely ignored.
.It pwc == NULL
.Fn mbtowc
executes the conversion as if
.Fa pwc
is non-null, but a result of the conversion is discarded.
.It n == 0
In this case,
the first
.Fa n
bytes of the array pointed to by
.Fa s
never form a complete character.
Thus, the
.Fn mbtowc
always fails.
.El
.\" ----------------------------------------------------------------------
.Sh RETURN VALUES
Normally,
.Fn mbtowc
returns:
.Bl -tag -width 012345678901
.It 0
.Fa s
points to a null byte
.Pq Sq \e0 .
.It positive
Number of bytes for the valid multibyte character pointed to by
.Fa s .
There are no cases where the value returned is greater than
the value of the
.Dv MB_CUR_MAX
macro.
.It -1
.Fa s
points to an invalid or an incomplete multibyte character.
The
.Fn mbtowc
also sets errno to indicate the error.
.El
.Pp
When
.Fa s
is equal to NULL,
.Fn mbtowc
returns:
.Bl -tag -width 0123456789
.It 0
The current encoding is state-independent.
.It non-zero
The current encoding is state-dependent.
.El
.\" ----------------------------------------------------------------------
.Sh ERRORS
.Fn mbtowc
may cause an error in the following cases:
.Bl -tag -width Er
.It Bq Er EILSEQ
.Fa s
points to an invalid or incomplete multibyte character.
.El
.\" ----------------------------------------------------------------------
.Sh SEE ALSO
.Xr mblen 3 ,
.Xr mbrtowc 3 ,
.Xr setlocale 3
.\" ----------------------------------------------------------------------
.Sh STANDARDS
The
.Fn mbtowc
function conforms to
.St -ansiC .
The restrict qualifier is added at
.\" .St -isoC99 .
ISO/IEC 9899/1999
.Pq Dq ISO C99 .
.Sh CAVEATS
On error, callers of
.Fn mbtowc
cannot tell whether the multibyte character was invalid or incomplete.
To treat incomplete data differently from invalid data the
.Xr mbrtowc 3
function can be used instead.